A traditional roly-poly toy (RPT), or “tumbler” toy, is a passive toddler's toy that can manage to stay upright despite apparent attempts to topple it. When physically disturbed, the RPT rocks about its typically rounded base, and perhaps is incidentally displaced a very short distance from place to place, but does not topple over. Failure to topple is due to the toy's bottom-heavy weight distribution. When the toy's positioning is disturbed, the toy rocks in an interesting manner and ultimately, absent further disturbance, returns to an upright position. FIG. 1 shows an example 5 of a traditional RPT. A traditional RPT has no locomotive capability.
The traditional RPT differs from various other types of apparatuses, including, for example, locomotive toy vehicles. Typically and traditionally, locomotive toy vehicles take the form of boats, airplanes, walking or crawling devices, or conventional multi-axle vehicles having wheels or “caterpillar” tracks. Locomotive toy vehicles may be remotely controlled (e.g., wirelessly by a human operator) or controlled autonomously via on-board navigation logic.
There have been some efforts made to create locomotive vehicles of relatively a typical design. For example, locomotive vehicles exist that are each supported and driven solely by a single roller—for example, a single ball-shaped wheel. FIGS. 2A-2B schematically show one example of such a conventional single-roller locomotive toy vehicle 10, called the “Sphericle”. The Sphericle 10 is a hollow sphere that has a conventional four-wheeled, dual-axle car 12 in its interior. As the wheeled car 12 attempts to drive “up” (as shown by arrow 14) the interior wall of the sphere 10, gravity on the wheeled car 12 causes the sphere to roll (as shown by arrow 16) relative to the ground, thereby causing the spherical 10 to achieve locomotion (as shown by arrow 18). The Sphericle is described further in Bicchi, Antonio, et al., “Introducing the ‘Sphericle’: an Experimental Testbed for Research and Teaching in Nonholonomy”, Proceedings of the 1997 IEEE International Conference on Robotics and Automation, Albuquerque, N. Mex., U.S.A., April, 1997.
Another example of a vehicle having only a single, spherical wheel is discussed in Koshiyama, A. and Yamafuji, K., “Design and Control of an All-Direction Steering Type Mobile Robot”, International Journal of Robotics Research, vol. 12, no. 5, pp. 411-419, 1993, hereinafter “Koshiyama et al.”. In Koshimaya et al., a single-wheeled locomotive robot includes a compact “arched body” above the wheel that is kept very stable by computer-directed stability control, such that “a cup of water placed on the top of the arched body of the robot could be carried without any spilling” (Koshimaya et al., left column, page 418). The robot of Koshimaya et al. touches the ground at its single wheel and also at two sensor arms that extend from the sides of the spherical wheel, at its axle ends, and trail on the ground.
Another class of vehicles having a typical design is the “parallel bicycle”, as recently exemplified by the much-publicized “Segway” vehicle, which is a vehicle that during use balances its body on only two parallel wheels that share a common axis of rotation. The body of the Segway vehicle is inherently unstable when driven, and the body is maintained in relatively upright position due to active computer-directed stability control. Under the stability control, an electronic computer receives positional sensor feedback and, based thereupon, gives rapid and frequent micro-bursts of drive power (including reverse or braking power) to the wheels in order to maintain an otherwise precarious balance. The balance is otherwise precarious such that, soon after the vehicle becomes un-powered, its body would lose balance and topple to touch the ground for direct support, for example, at a kickstand of the body, if the kickstand is extended. The Segway vehicle is further discussed in U.S. Pat. No. 6,367,817. (“Segway” is a trademark of its owner.)